An inspection device including a probe pin has been used to inspect the electric characteristics of a semiconductor integrated circuit such as an integrated circuit (IC) chip. The inspection device inspects the electrical conductivity of a test object by pressing multiple probe pins against the test object. An example of such probe pins included in the inspection device is described in Patent Literature 1.
The probe pin described in Patent Literature 1 includes a first plunger and a second plunger, which are semi-cylindrical and engageable with each other, and are contained in a conductive contact holder. Patent Literature 1 describes the first and second plungers that increase their area of contact as the plungers slide over each other in the axial direction of a spring member (refer to FIG. 1 in Patent Literature 1).